This proposal is in response to Notice Number NOT-OD-09-088 of the American Recovery and Reinvestment Act of 2009. We request funding for the first two years of the revised grant application 1R01AI73718-01A2, with changes in scope approved by the NIAID Program Officer. Specifically, we propose to elucidate the molecular mechanism of signaling by DAP10/DAP12/FcR[unreadable]-associated activating receptors (DAP- AARs), such as NKG2D in NK cells and integrins in myeloid cells, and to establish the role for several genes encoding proteins essential for mediating signals emanating from DAP-AARs as susceptibility loci in microbial pathogenesis. In this context, we have recently identified critical new functions of Vav and DAP10/DAP12/FcR[unreadable] proteins in transducing signals emanating from innate immune receptors including activating receptors in NK cells and myeloid cells. Based on these preliminary data, we propose a model in which Vav and Phosphoinositide 3-kinase (PI3K) engage in crosstalk to amplify signals leading to NK cytotoxicity. The concept that Vav proteins control innate immune responses by activating both ITAM- and non-ITAM-dependent signaling represents a novel paradigm in signal transduction and cellular activation. In this context, striking new findings from several labs including ours reveal a previously unanticipated mechanism in which integrins and other adhesion receptors utilize DAP12 and FcR[unreadable] to promote both adhesion and effector responses. While the augmentation of neutrophil effector responses including cytokine production, degranulation, and phagocytosis by adherence to integrin ligands has been appreciated for over 30 years, these new results reveal shared signaling modules activated by both proinflammatory stimuli and adhesion receptors. In this modified proposal, we aim to establish the mechanism of NKG2D- DAP10-proximal signaling and Vav1-PI3K crosstalk (Aim 1), and to delineate signaling pathways emanating from the DAP10/DAP12/FcR[unreadable]-associated activating receptors (DAP-AARs) and establish the role for several genes encoding proteins essential for mediating signals emanating from DAP-AARs as susceptibility loci in microbial pathogenesis in vivo (Aim 2).